Fuse size for starter

[Mickeyrouse]

I have just about everything on our boat protected by a fuse. Lately I’ve been wondering about the fuse rating used on the engine starter. The engine is a Westerbeke 55B4- nothing extravagant or esoteric. When the engine was first installed I added a 200 amp fuse in series on the positive cable to the starter. After using the engine about 3 months the fuse blew in the process of a routine start, so I increased to a 250 amp. No other issues in the 12 years since.
Lately I’ve been thinking about a circuit breaker there, but I find nothing in that rating.
What size do I really need to protect the starter?

[boatpoker]

Originally Posted by Mickeyrouse

I have just about everything on our boat protected by a fuse. Lately I’ve been wondering about the fuse rating used on the engine starter. The engine is a Westerbeke 55B4- nothing extravagant or esoteric. When the engine was first installed I added a 200 amp fuse in series on the positive cable to the starter. After using the engine about 3 months the fuse blew in the process of a routine start, so I increased to a 250 amp. No other issues in the 12 years since.
Lately I’ve been thinking about a circuit breaker there, but I find nothing in that rating.
What size do I really need to protect the starter?

I've been running this 300amp MRBF fuse on the starter battery of a Westerbeke 55A for 6 years without issue.

https://www.bluesea.com/products/519...al_Fuse_-_300A

[Jammer]

It is not usual practice to provide overcurrent protection on the starter lead.


I have a magnetic ammeter, not very accurate but useful for high currents, on 6 cylinder agricultural diesels in cold weather 300-600 amps is not unusual.


The real question is what sort of fault are you trying to protect yourself against?


Insulation failure on the starter cable is the hardest. I've seen these and they are dramatic, insulation burns away, smoke everywhere, ordinarily no fuse. Eventually the battery is dead and the drama stops. That's on machines made of iron and steel. On a fiberglass boat the hazard is reduced, less to short out against.


The question is whether such a failure would draw enough current to blow a fuse or trip a breaker. Maybe, but often not.


Perhaps a better move is to sleeve the starter lead and inspect it every year.


Low resistance shorts to ground in the starter itself or its solenoid are vanishingly rare.

[Sailmonkey]

Originally Posted by Mickeyrouse

Lately I’ve been thinking about a circuit breaker there, but I find nothing in that rating.

What size do I really need to protect the starter?

You can’t find a breaker?

https://www.google.com/search?q=250+...&client=safari

You’re protecting the wire, not the starter.

[boatpoker]

Rod Collins has an excellent article on why your starter battery positive conductor should be fuse protected. Make sure you read all the way down to the photo of the burnt out boat that did not have such protection.

https://www.pbase.com/mainecruising/battery_fusing

[phorvati]

Originally Posted by Sailmonkey

You can’t find a breaker?

https://www.google.com/search?q=250+...&client=safari

You’re protecting the wire, not the starter.

Exactly, melted wire insulation is the one that would start a fire. I have 500A ANL fuse on a 2/0 gauge wire to my starter. 90HP Ford Lehman.

[Frankly]

Keep in mind that a fuse in the starter circuit is most likely to protect against a short circuit/ ground fault rather than an overload. Bumping up the size a little is not going to make a significant increase in the clearing time under fault conditions. Also type ANL are somewhat slow on the blow.

250 amp on my Yanmar 3GM


Frankly

[Bycrick]

200 amp fuse with 2/0 wire on a Yanmar 4JH2. 175A on several 3GM4s. Never had one blow.

A 500a ANL fuse will pass 650-700 amps for tens-of-minutes. That’s way more than enough for 2/0 wire you burn. I think that’s way to big a fuse.

[skipmac]

Originally Posted by boatpoker

Rod Collins has an excellent article on why your starter battery positive conductor should be fuse protected. Make sure you read all the way down to the photo of the burnt out boat that did not have such protection.

https://www.pbase.com/mainecruising/battery_fusing

Exactly the reason I fused my starter cable. Like many potential problems on a boat the odds of this happening are small but the down side if it does is large. Cheap and easy insurance against fire in the engine room

I've been using a 250 amp MRBF fuse for five years now without a problem. Even when I had some unnoticed corrosion on the cable to the starter which caused hard starting and higher draw from the batteries

[Cadence]

Originally Posted by Mickeyrouse

I have just about everything on our boat protected by a fuse. Lately I’ve been wondering about the fuse rating used on the engine starter. The engine is a Westerbeke 55B4- nothing extravagant or esoteric. When the engine was first installed I added a 200 amp fuse in series on the positive cable to the starter. After using the engine about 3 months the fuse blew in the process of a routine start, so I increased to a 250 amp. No other issues in the 12 years since.
Lately I’ve been thinking about a circuit breaker there, but I find nothing in that rating.
What size do I really need to protect the starter?

Stick with the fuse and keep some spares.

[Kokanee]

I have a 200amp ANL fuse on my 42 hp Vetus and have not blown it yet. Seems about right for a 4 cylinder diesel.

[oleman]

Our 24 volt engine system with a 505 CI diesel and a MT42A starter has an 800A fuse at the battery bank. I discovered that was an expensive when some Techs managed to blow it!

[SteelEagle]

We have a 300A ANL fuse on a 2/0 wire to our 3.9L Isuzu. Haven't blown it yet, but we do keep spares on hand.

[seabreez]

Originally Posted by Sailmonkey

You can’t find a breaker?

https://www.google.com/search?q=250+...&client=safari

You’re protecting the wire, not the starter.

I just finished re-wiring two vessels. one a tug boat and a second one a small cruise ship. The main wiring battery cables now have to be fused as close as possible from the battery (less than two feet) as per the code. I agree with Sailmonkey that the fuses or breakers are there to protect the wiring and not the accessory it supplies...

[sailorboy1]

I have a 200amp fuse on my starter battery. This is not i feel something to have a breaker instead. The only advantage a breaker has is you can reset it. But blowing a 200 amp fuse is a serious thing and i see no plus to being able to “just reset it”. It has only 1 function, prevent a short from starting a fire.